The present invention relates to endovascular stents and more particularly pertains to coatings that are applied to stents in order to reduce thrombogenicity.
Stents are implanted within blood vessels in an effort to maintain their patency by preventing collapse of the lumen and/or by impeding restenosis. Unfortunately, the presence of a foreign object within the blood flow may have a thrombogenic effect. It has therefore been found to be desirable to use various anti-coagulant drugs in an effort to reduce the likelihood of the development of restenosis and provide an antithrombogenic effect.
A drug that has been found to be particularly effective for such purpose is heparin. By maintaining an effective concentration of the drug in and about the implantation site until the stent is encapsulated by tissue, the risk of thrombogenesis is substantially mitigated. To that end, various approaches have been employed in the administration of heparin.
While the systemic administration of heparin can cause the implantation site to be subjected to an effective level of heparin, such level of heparin would necessarily also be present throughout the rest of the body which can lead to undesirable side effects such as bleeding. It has therefore been recognized that a regimen wherein the heparin is substantially constrained to the implantation site is far more desirable. An approach that has been devised to achieve such end requires the coating or impregnation of the stent itself with heparin. The heparin is thereby concentrated where it is most needed while its presence, and consequently its effect, throughout the rest of the body is minimized.
Disadvantages associated with heretofore known heparinized stents include, the limited shelf life of such devices, the fact the heparin is degraded when the stent is sterilized either by heat or by exposure to ethylene dioxide, the inability of the physician to alter the dosage that the patient is subjected to and the inability to replenish any heparin that may be lost while the device is deployed. Additionally, the cost of heretofore known heparinized stent devices has been very high as it necessarily includes the costs associated with the stringent regulatory requirements attendant a drug containing device.
The prior art has been unable to overcome these disadvantages and shortcomings and a new approach is needed to safely, effectively, and economically deliver heparin to an implantation site.